β-Subunit of Nuclear Pore-targeting Complex (Importin-β) Can Be Exported from the Nucleus in a Ran-independent Manner*
- From the ‡Department of Anatomy and Cell Biology, Osaka University Medical School, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan and the §Department of Biotechnology, Graduate School of Agriculture and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
Abstract
The nuclear export of importin-α is mediated by CAS, which is related to importin-β, whereas the mechanism for the export of importin-β remains unclear. In this study, we demonstrate that the nuclear export of importin-β is mediated by the nuclear pore complex-binding domain of this molecule. Insensitivity to leptomycin B indicates that its export is not mediated by a leucine-rich nuclear export signal-specific receptor, CRM1. Furthermore, the nuclear export of importin-β was not inhibited by co-injection with a GTPase-deficient Ran mutant (G19V). The cell line tsBN2 contains a temperature-sensitive point mutation in the RCC1 gene, which encodes a guanine nucleotide exchange factor of Ran. At the nonpermissive temperature, importin-β was exported from the nucleus of these cells, even when RanGAP1, a GTPase-activating protein for Ran, was co-injected. These results not only provide support for the view that Ran-dependent GTP hydrolysis is not required for the nuclear export of importin-β but also indicate that nuclear RanGTP is not essential for its export. As a result, we propose that importin-β can be recycled from the nucleus alone in a Ran-independent manner.
Footnotes
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↵* This work was supported by Grant-in-aid for Scientific Research on Priority Areas 07282103, Grant-in-Aid for Scientific Research (B) 08458229, Grant-in-Aid for Scientific Research (C) 08680764, and Grant-in-Aid for COE Research 07CE2006 from the Japanese Ministry of Education, Science, Sports and Culture, the Nissan Science Foundation, and the Naito Foundation.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵¶ To whom correspondence should be addressed. Tel.: 81-6-6879-3211; Fax: 81-6-6879-3219; E-mail:yyoneda{at}anat3.med.osaka-u.ac.jp.
- Abbreviations:
- NPC
-
nuclear pore complex
- BSA
-
bovine serum albumin
- GFP
-
green fluorescent protein
- GST
-
glutathione S-transferase
- HVJ
-
hemagglutinating virus of Japan
- NES
-
nuclear export signal
- NLS
-
nuclear localization signal
- PTAC
-
nuclear pore-targeting complex
- TR
-
Texas Red
- WGA
-
wheat germ agglutinin
- WT
-
wild type
- PCR
-
polymerase chain reaction
- DTT
-
dithiothreitol
- PBS
-
phosphate-buffered saline
- aa
-
amino acid(s)
- T-APC
-
SV40 large T-antigen NLS conjugated to allophycocyanin.
-
- Received August 18, 1998.
- Revision received November 9, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
